Construction machinery such as excavator may use various attachments under work conditions. For example, a bucket may be used for an excavation work or a ground leveling work, and a breaker may be used for a stone crush work.
When the bucket is used, the bucket may move forward and backward to perform the ground leveling work. For the ground leveling work, the force of the bucket acting on a ground may need to be maintained constant. Accordingly, a precise and accurate control of a boom and the bucket may be required and thus an operator feels tiredness with the manipulation.
When the breaker is used, the boom may be bounded by reaction force when the breaker crushes stone. Accordingly, the force of the breaker acting on the stone may need to be maintained constant and a precise and accurate control of the boom and the breaker may be required.
On the other hand, a hydraulic pump may supply a working oil to a rod side of a boom cylinder to lower the boom. On this occasion, the boom may descend faster than intended because of inertia load of dead load of the boom and the bucket. That is, a speed of the working oil discharged from a cylinder rod side of the boom cylinder may be greater than a speed of the working oil supplied from the hydraulic pump to a cylinder head side of the boom cylinder. Thus, a cavitation phenomenon within the cylinder rod side of the boom cylinder may occur.